Various types of memories are proposed as nonvolatile semiconductor memory devices for storing data in a memory cell in a nonvolatile manner. Among them, a NAND type flash memory is widely used as a data storage device because its memory capacity can be increased easily.
In order to further increase access speed, a NAND type flash memory capable of performing a so-called interleave operation is proposed. An interleave operation is an operation method in a NAND type flash memory having a plurality of memory cores. It executes an operation in one of the memory cores while executing another operation (for example, a pre-charge operation) in another of the memory cores, for example. This may conceal an operation in one memory core, and as a result increase the access speed as a whole.